Control system



F. MOHLER 2,264,095

CONTROL SYSTEM Fild Dec. 1a, 1936 s Sheets-Sheet 1 7 H J 4 H I V 2 III M l ll II |||l|,l A a 2% 6 a 2 0.\ L 6 6 a 4 my a n Inventor: Francis Mahler" b W 6} Hi5 Attorneg Nov. 25, 1941. F. MOHLER CONTROL SYSTEM Filed Dec. is, 1936 s Sheets-Sheet 2 Inventor:

0 .56 m w E l5 Attornqg- Nov. 25, 1941. F. MOHLER CONTROL SYSTEM Filed Dec. 18, 1936 3 Sheets-Sheet 3 Inventor. Francis Mohler,

I H is Attorneg- Patented Nov. 25, 1941 FFlCE CONTROL SYSTEM Francis Mohler, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application December 18, 1936, Serial No. 116,656

22 Claims.

This invention relates to control systems, more particularly to systems for controlling apparatus having an element for performing an operation on a length of material under tension, and it has for an object the provision of a simple, reliable and improved system of this character.

More pecifically the invention relates to rolling mill apparatus and the like having means for reducing the gauge or thickness of a length of material and an element for maintaining the material under tension while its gauge is being reduced, and a more specific object of the invention is the provision of. improved means for maintaining the gauge of the worked material substantially constant.

In the practice of rolling cold strip material for example, it is highly desirable to maintain a constant thicknes of the rolled strip as nearly as possible or, in other words, constant gauge is of extreme importance. The trade is becoming very rigid in the allowable tolerances or variations in gauge. Even withthe present precision worked material.

In illustrating the invention in one form thereof, it i illustrated as embodied in a control system for a rolling mill having a pair of rolls for mills which are equipped with very accurate continuous gauges for measuring the strip thickness at all times, all of the sheets must be sorted and a fairly high percentage is either thicker or thinner than the allowed tolerance.

These mills are equipped with screw-down mechanism for raising and lowering the top rolls and are equipped with tension devices for maintaining substantially constant tension in the strip as it is wound up on drums or reels after emerging from the mill. Some of the mills are of the continuous type utilizing a plurality of stands followed by a reel, and some are of the reversing type utilizing a reel on either side of.

the mill for winding up and unwinding the strip respectively,'and vice versa. The type of mill, however, is immaterial, since the invention is applicable to all types.

In carrying the invention into efiect inone form thereof, means are provided for responding to variations in the gauge of material being worked under tension to vary the tension so as to maintain the gauge substantially constant.

More specifically, as applied to apparatus having an element for reducing the gauge of a length of material and a device for .ensioning the material, a dynamo-electric machine is mechanically coupled to the tensioning device, and a current regulator is provided'for maintaining the current of the dynamo-electric machine substantially constant at a set value together with means responsive to variations in the gauge of the worked material for varying the setting of all reducing the gauge of a strip of material, a takeup reel, and driving means for the reel so controlled as to maintain the strip under tension between the rolls and the reel. For abetter and more complete understandingof the invention, reference should now be had to the follow-' ing specification and to the accompanying drawing in which Fig. 1 is a simple diagrammatical sketch of an embodiment of the invention and Figs. 2 and 3 are modifications.

Referring now to the drawings, the thickness of a length'of material I0 is being reduced by suitable means illustrated as comprising a pair of rolls ll. .Rolls H are driven by any suitable driving means such, for example, as an electric motor (not shown). The length of material ID is delivered from the rolls H in the direction of the arrow and is wound upon a, reel I 2 driven by suitable means illustrated as a direct current electric motor l3.

Motor I3 i supplied from a pair of buses M which are connected to a suitable source when a switch I5 is moved to its closed position. As shown, motor I3 is provided with a field winding 5 which is also connected to the bus M. Suitable starting means are provided for connecting the motor I 3 to the source and for accelerating the motor to full speed. Motor starters used in actual practice are often quite complicated. They may beof the rheostatic type with a number of sections of resistance and a plurality of accelerating contactors for short circuiting the resistance sections, or they may be of the adjustable voltage type, in which case the voltage of a generator is controlled so as to start and stop the reel motor. However, since the specific structure of the starting means constitutes no part of the present invention, it is illustrated simply as comprising an electromagnetic contactorl1 and a switching device, preferably a manually operated -pushbutton type switch l8, for controlling its energization.- For the purpose of maintaining the tension in the strip between the rolls II and the reel l2 substantially constant at a predetermined value, means illustrated as a constant tension between the mill rolls and the reels substantially constant at constant strip speed, it is necessary gradually to increase the excitation of the motor l3 o as to maintain the armature current constant. This is accomplished by the regulator I9. Although regulator l9 may be of any suitable type it is shown as a vibratory contact type regulator. Briefly, regulator l9 comprises stationary contact and a movable contact 2| arranged for alternately short circuiting and removing the short circuit from a resistance 22 included in the field circuit of reel motor l3. A core member 23 is pivotally connected to the arm which carries the movable contact 2| and is arranged within the turns of a solenoid 24 which in turn is connected so as to be responsive to the current flowing in the armature circuit of reel motor I3. A spring 25 is attached to the movable contact arm 50 that its pull opposes the pull of the'solenoid on the core. A second coil 26, referred to as a bias winding, is also provided and arranged to act on the core 23. The operation of the regulator is briefly as follows: With the machine |3 operating as a motor, an increase in the armature current of the motor I3 above the predetermined value causes the contacts 2|, 20 to close against the tension of the spring 25 and thereby to short circuit the resistance 22. This increases the excitation of the motor l3 and causes its speed to decrease until the armature current becomes less than the predetermined value at which time the pull of the spring 25 overpowers the pull of the solenoid and separates the contacts 20, 2| to remove the short circuit about resistance 22. Reinsertion of the resistance 22 in the field circuit of motor |3 decrease the excitation of the motor and causes its speed and armature current to increase. The reel motor armature current continues to increase until it exceeds the predetermined value and again causes the contacts 20, 2| to close and short circuit the resistance 22. The foregoing operation is repeated at a very rapid rate and thus the regulator tends to vibrate to hold a fixed or constantcurrent in the reel motor armature. A tension adjusting rheostat 21 is included in the circuit of the .current winding. If this rheostat is ad- 'justed to increase the resistance in series with the winding, more current in the reel motor armature will be necessary to obtain the required current in the current winding and therefore the actual current maintained in the reel motor armature can be increased and decreased by varying the resistance in series with the current winding. For all values of tension, however, the current in the current winding remains at a fixed value.

The purpose of the bias winding 26 is to provide for changing the setting of the regulator a fixed percentage of the tension being maintained for a predetermined increment adjustment of a controlling rheostat 28. As shown, this controlling rheostat 28 is included in circuit with the bias winding '26 across the buses l4. Winding 26 iswound so that it assists the winding 23 in opposing the pull of the spring 25. Since the pull of the two coils is in the same direction, the pull required from the current winding 24 is decreased by the amount of the pull supplied by the bias winding. Thus, if the bias winding supplied 10% of the pull, only of the pull will be required from the current winding in order to balance the spring and, in turn, only 90% of the current will be required through the reel motor armature to produce this 90% pull; This is true irrespective of the actual value of the tension for which the tension adjusting rheostat 21 is set because, as stated in the foregoing, the current in the current winding remains fixed at a substantially constant value, irrespective of the tension being maintained. Thus if the tension adjusting rheostat 21 is set for 20,000 lbs. tension, and the bias winding supplies 10% of the pull, the actual tension maintained by the regulator will be 18,000

lbs. On the other hand, if the tension adjusting rheostat is set to hold 10,000 lbs. tension, and 10% of the pull on the regulator is supplied by the bias winding, the actual tension maintained will be 9,000 lbs.

If the control rheostat 28 is sufficient to vary the pull of bias winding 26 from practically zero to a substantial value such, for example, as 50% of the pull required for the regulator, equal increment adjustment of this rheostatwill always represent the same'percentage change of the tension being maintained, irrespective of the setting of the tension adjusting rheostat. This feature is desirable because if the strip is thick and a high tension is being maintained, the increment adjustment of the tension should also be relatively high as compared with the case when the strip is thin and relatively low tensions are being maintained.

For the purpose of continuously measuring and indicating the thickness of the material III, a suitable gauge 29 is provided. Although several types of gauges and other devices satisfactory for thi purpose are available on the market, it is preferred to employ a variable air gap transformer type gauge. This type of gauge has a pair of contact rolls 30, one above and one below the strip. One of these rolls, preferably the lower roll, is fixedly mounted, and the other roll is mounted for movement with respect to the first roll in response to changes in the gauge of the strip. These rolls press on the strip at all times, and the movement of one with respect to the other is a measurement of variations in the thickness of the strip. This movement is transmitted to the movable magnetic vane member 3| of an air gap transformer type gauge head and, by means of a power unit which includes the necessary rectifying means 32, anindication of the strip thickness is given on a microammeter- 33 which is calibrated in any convenient unit of strip thickness. This type of gauge is well known to the trade, and since its specific internal structural details constitute no part of the present invention, a more detailed description is omitted.

The electric gauge indicating instrument 33 is preferably equipped with a zero-center movable contact member 34 and two stationary contacts 35 and 36. In practice, these two stationary contacts preferably take the form of mercury cup contacts, the positions of which are adjustable with respect to the central position of the movab1e 'contact member 34. The movable contact member makes contact with the mercury cup on either side of the zero position and this circuit closing feature i utilized for actuating the control. The gauge is provided with means for initial adjustment so that the movable contact member 34 will be in the zero position when the contact rolls 30 are separated a distance equal matic adjustment.

to the desired thickness of the strip. Oversize calibrations are on one side of the zero position, preferably the right side, and the undersize calibration are on the left side. Thus, if the strip is running at the correct gauge, the instrument will indicate zero, but if it runs oversize, the movable contact member will swing to the right in proportion to the amount of the oversize, and

conversely, if the strip is running undersize, themovable contact member will swing to the left.

The mercury cup contacts can be adjusted in position so that they make contact with the movable contact member at any desired point. In other words, if the total scale deflection to the right represents .005 inch the mercury cup can be adjusted so that it will make contact when the instrument indicates .005 inch, or any other desired point such as .002 inch. Thus the setting of the mercury cup depends upon the tolerance which is to be allowed.

Various mechanisms are available for operating the screws so as to raise and lower the top rolls. For the purpose of illustration, a simple screw gearing 31 and a direct-current-motor 38 for driving the screw are indicated in the drawing.

In this specification the term increment is to be understood as the length of time, or amount that the screws are raised or lowered or, when referring to tension, increment" is to be understood as the length of time or amount the tension is increased or decreased upon each auto- When an indication for correction is given, a second correction should not be made until the effect of the first correction is measured. The time required for the correction to be measured depends upon the distance between the mill rolls and the gauge as well as the time required for making the adjustment. Since the distance between the gauge and the rolls remains fixed, this part of the interval always represents a constant length of strip. That part of the interval which is dependent upon the time required to make the increment adjustment is variable'ln terms of the length of strip. Therefore, if the increment adjustment requires .25 second irrespective of the speed of the mill, more strip will pass through the mill when operating at maximum. strip speed than when operating at minimum strip speed. Thus, if the intervals are measured as a function of length of strip, the length which passes through the mill during the longest increment adjustment andat the maximum speed must be taken into account.

For determining the intervals, a limit switch 39 is provided. This limit switch is connected either directly or through gearing to the mill rolls in such a manner that one revolution of the limit switch represents the length of strip which must pass through the mill between successive increment adjustments. Relay means 40 controlled V by the gaugecontacts 34, 35, 36 serve to control a pilot motor 4| which rotates the movable contact arm. 28a. of the rheostat 28 in the circuit of the biasing coil 26 of the tension regulator. This relay apparatus comprises a switching device 42 and its timing device 43, 1'or controlling the rotation of the motor 4| in such a direction as to increase the tension setting of the regulator, and

- a switching device 44 and its timing device 45 for efi'ecting rotation of the motor 4| in the opposite direction to decrease the tension setting of the regulator. Switching devices 42 and 44 are illustrated as electroragnetic contactors, and timing devices 43 and 45 are illustrated as inducenergizing circuit for the contactor 42.

tation of the screw-down motor 38 in a direction to increase the opening between the mill rolls II and an electromagnetic contactor 49 and its timing relay 50 for effecting operation of the screwdown motor 38 in a direction tolower the top roll and thereby to decrease the opening between the mill rolls.

Means, illustrated as comprising limit switches 5|, 52, and 53, and corresponding selector switches 54, 55, and 56, are provided for maintaining the screw actuating mechanism inactive in response to variations in the gauge of the material until the tension regulating mechanism has varied the tension a preselectable percentage of the value the tension regulator is set to hold.

With the foregoing understanding of the elements and their organization in the complete control system, the operation of the system itself will readily be understood from the following detailed description: The system. is placed in condition for operation by closing the line switch l5 to energize the buses' l4. This completes an energizing circuit for the timing relays 43, 45, 48 and 50. The energizing circuit for timing relay 43 is traced, from the upper bus l4 through the upper contact of contactor 42, through coil of relay 43 to the lower bus I 4. Similar energizing circuits for timing relays 45, 48 and 50 are obvious. In response to energization, timing relays 43, 45, 48 and 50 close their contacts.

The reel motor I3 is started by depressing the start button switch I 8 to close its contacts and -input to the armature of reel motor l3. Switch 51 is closed to place the system in condition for automatic operation.

As long as the gauge of the strip remains within the predetermined tolerances for which the gauge 29 is set, the bridge circuit in the head of the gauge 29 remains balanced and no voltage is supplied to the contact-making microammeter 33. However, if the strip l0 should begin to run oversize, the movable contact member 34 will swingto the right and make contact with the stationary contact 36 partially to complete an This circuit is completed when the conducting segment 39a of the limit switch makes contact with the brush 33b. The circuit is traced from the upper bus l4 through the limit switch 39, switch 51. lower contact of contactor l1, conductors 58 and 59, movable ary contact member 36, conductor 60, operating coil of contactor 42, and thence by conductor GI to the lower bus I 4. Contactor 42 closes in response to energization, and its closing completes a circuit through the armature of the rheostat motor 4| and its series split field winding 4h.

As shown,

contact member 34, stationlimit switch has rotated out of contact with thebrush 39s. 'This holding circuit is traced from the upper bus l4 through conductor 62, intermediate contact of contactor 42, contacts of time delay relay 43, conductor 63, conductors 58 and 59, contacts 34 and 36, conductor 60, operating coil of contactor 42 and conductor 6| to the lower bus l4. Contactor 42 in. closing interrupts the energizing circuit for the time delay relay 43 and after an interval of time determined by the adjustment of the time delay relay 43, this relay opens its contacts to interrupt the holding circuit for the contactor 42 which thereupon opens its lower contacts to interrupt the armature circuit of the rheostat motor 4|. Movable contact'arm 28. of the rheostat comes to rest after having increased the resistance in circuit with the bias winding of the regulator. The result is that a larger current must flow in the armature circuit of the reel motor in order to produce sufiiclent current in the current winding '23 of the regulator to balance the pull of the spring 25. This increased armature current also increases the tension in the strip between the mill rolls H and the reel I2 and the effect of this increased tension is to reduce the gauge of the strip.

After an interval of time sumcient for a point on the strip to pass from the mill rolls II to the gauge contact rolls 30 has elapsed, conducting segment 399, of the limit switch again rotates into engagement with the brush 39b and if the increased tension in the strip has not reduced the thickness to within the required tolerance the foregoing operation is repeated.

If, on the other hand, the increment adjustmentsof tension were sufiicient to bring the material down to the proper gauge, the mercury cup contacts 34, 36 will be separated and the contactor 42 will not reclose the next time the conducting segment 38a. of the limit switch 39 rotates into engagement with the stationary bus 39b, and no further increment adjustment in the tension of the strip will be made.

If the strip runs undersize, the movable cona similar manner. However, .this contactor and its relay cannot energize the screw-down motor 38, unless one of the selector switches 54; 55, 56, is closed and the conducting segment of one of the corresponding limit switches 5|, 52, or '53 is in engagement with its cooperating stationary brush. For example, assume that the switch 55 is selected and closed by the operator. When the motor operated rheostat 28 has rotated the contact arm 289, through an arc of 90 in the increase direction, an energizing circuit for the "down contactor 68 will be established from the lower bus |4 through the limit switch 52 on selector switch 55, conductor 64, upper contact of contactor 49, operating coil of down contactor 68 to the upper bus l4. Contactor 68 will close in response to energization and connect the screw-down motor 38 to the supply source for rotation in a direction to lower the top roll H and thereby to decrease the opening between the rolls. After a predetermined interval of time determined by the setting of the time delay relay 50, the relay 50 functions in ,a manner similar to the relay 43 to deenergize the contactor 49 which thereupon opens its contacts to deenergize the coil of the down contactor 68, and contactor 68 in turn opens its contacts to disconnect the screw-down motor 38 from the supply source. If the correction so made is insu-flicient to restore the thickness of the strip to the required tolerance this action is repeated each time the contact member 34 will make contact with the left-,

hand mercury cup contact and this will cause the contactor 44 and timing relay 45 to function in a manner similar to that described for contactors 42 and 43, to energize the rheostat motor 4| for rotation in a direction to decrease the amount of resistance in the bias winding of the regulator and thereby to decrease the tension in the strip between the rolls II and the reel [2. This decreased tension will cause the gauge of the strip to increase, and the operation of the contactor 44 and the timing relay 45 under the control of the limit switch 39 and the gauge will be repeated until the thickness of the strip is within the required tolerance.

During the time that the contactor 42 and its timing relay 43 are functioning to increase the tension in the strip the screw lowering contactor 49 and its time relay 50 are also functioning in ducting segment of the limit switch 39 rotates into engagement with the stationary brush 39b.

If the thickness of the strip should be less than the required tolerance the contactor 41 and its timing relay 48 will function in a similar manher to energize the up contactor to close its contacts and connect the screw-down motor 38 to the source for rotation in a direction to raise the top roll II to increase the distance between the rolls. After an interval of time determined by the setting of the time delay relay 48, the contactors 41 and 65 will be deenergized and the screw-down motor 38 disconnected from the supply source. It will, of course, be understood that the operation of the contactor 41 and its timing relay 4B is analogous to that of the contactor 49 and its timing relay 50. That is to say, contactor 41 will not energize the up con tactor 65 until'the tension in the strip has been decreased a predetermined amount and the limit switch 52 has been rotated through an arc of 90 from the position in which it is shown in the drawings.

If, on th other hand, selector switch 56 is closed the motor operated rheostat 28 would have to turn through an arc of 135 either in the tension increase or tension decrease direction, before the screw-down motor 38 could be energized to raise or lower the rolls.

Thus, means are established for first increasing or decreasing the tension in the strip up to a certain preselectable percentage of the value which the tension regulator is set to hold, and then lowering or raising the top mill roll in preselectable increments.

At the completion of the rolling of the strip or at the completion of a pass. it is desirable to return the motor operated rheostat 28 to its first position so that the basic adjustment of the tenson by the main tension adjusting rheostat 21 is always the-same. This is accomplished by means of limit switches 66 and 61 connected to the shaft of the motor operated rheostat. It will be noted that as soon as the reel motor is ing brushes. When thiscondition obtains, the,

rheostat motor 4| is brought to rest with the movable rheostat arm 289. in the central position in which it is shown and the limit switches 52 and 53 in the positions in which they are shown in the drawing.

An obvious modification of the scheme shown in Fig. 1 is to stop the increment adjustments of tension as soon as the increment adjustments of the screwdown are started.

For small variations in gauge, corrections can usually be made by. varying the tension alone. However, upon greater variations it is necessary to adjust the screws as well as to vary the tension of the strip. In the modification of Fig. 2, means are provided for making corrections in the tension alone when the variations in the gauge are relatively small, and additional means are provided for simultaneously energizing the screw-down mechanism to raise or lower the top roll, when the variations in the gauge are relatively large. The arrangement disclosed in the modification of Fig. 2 is substantially identical with th arrangement disclosed in Fig. 1, but difiers from it primarily in that the contactors and relays which control the screw-down motor are controlled by means of a second microammeter I8 supplied from the gauge head instead of being controlled by a plurality of limit switches operated by the rheostat motor cooperating with the indicating microammeter which controls the tension'adjusting mechanism. Thus it will be noted that that portion of the modification disclosed in Fig. 2 of the drawings which is above the dotted line II is identical with a corresponding portion of the modification of Fig. 1. In the portion of the modification of Fig. 2 below the dotted line H, limit switch mechanisms corresponding to limit switches 5|, 52 and 53 are omitted and contactors I2 and I3 corresponding to contactors 41 and 49 of Fig. 1 and timing relays 14 and I5 corresponding to relays 48 and 58 of Fig. 1 are directly controlled from the microammeter I8 supplied from the power unit in the head of the gauge Hi. In addition to a limit switch 11 for preventing repeated increment adjustment operation of the tension adjusting mechanism until a predetermined length of strip I8 has passed the contact rolls I9 of the gauge after an increment adjustment has been made, an additional limit switch 88 mounted on the shaft of the limit switch I1 is provided for preventing a repeated actuation of the screw-down mechanism until a predetermined length of strip has passed the contact rolls I9 of the gauge after an increment adjustment has been made in the position of the top roll 8|.

The contact making microammeter I8 is provided with adjustable position mercury cup contacts 10a and 18b and with a movable zero center contact 18. Similarly, the contact making microammeter 82 is provided with stationary adjustable position mercury cup contacts 82a and 82b and with a movable contact member 82c.

The mercury cup contacts .823 and 82s are adjusted so that the movable contact member 82 will make contact with one or the other of the mercury cup contacts upon small variations in the gauge of the trip. The gauge I8 then controls the tension increment adjustment in a manner identical with that described in connection with the modification of Fig. 1. However, the mercury cup contacts 10a and T81 of the second contact making microammeter III are adjusted so as to make contact on greater variations in gauge.

This in turn controls the increment adjusting contactors 83 and 84 for the screw-down motor 85 in a manner similar to that described for the tension increment adjustment.

Thus, if the variation is great, no time is wasted in making several tension increment adjustments before making an adjustment in position of the top roll. On the contrary, an adjustment of the top roll is made immediately and simultaneously withthe increment adjustment in tension of the strip. As soon as the large variations have been corrected, the small variations will be corrected by tension alone. Otherwise, the operation of the modified system of Fig. 2 is identical with the operation of the system of Fig. l.

The modified system of Fig. 3 is similar to the systems disclosed in Figs. 1 and 2 but difiers from these systems primarily in that the contact making microammeter 86 is provided with a plurality of stationary contacts on each side of the central zero position of the movable contacts 86. for the purpose of producing increment adjustments of the tension of the strips and the position of the top roll 81 more nearly proportional to the amount of adjustment required. Thus, if the variation is slight, the time setting for the increment adjustment will be rather short. If the variation and strip thickness are somewhat greater, the time setting of the increment adjustment will be. proportionally increased. The contact making microammeter is illustrated as provided with three stationary contact members 86b, 86 and 85a to provide three degrees or amounts of increasing increment adjustments, and three stationary contacts 86a, 88: and as; to

provide three degrees or-amounts of decreasing increment adjustments.

The means for controlling the tension increment adjustments comprises contactors 88 and 89 and their timing relays 98 and 9| respectively. The means for efiecting increment adjustments in the position of the top roll 81 comprises contactors 92, 93 and their respective timing relays 94 and 95. Contactors 88, 89 and 92, 93 correspond in structure and in function with the contactors 42, 44 and 49, 41 respectively of Fig. 1. Similarly, timing relays 98, 9| and 94, 95 correspond with timing relays 43, 45 and 58, 48 respectively of Fig. 1. The timing relays 98, 9| and 94, 95 are difierent from Fig. 1,.however, in that means are provided for changing the time constants of these relays. These means are illustrated as bucking coils 90a, 9'8, 94a. and 95s.

Additional means are provided for varying the .change of the time constants of these timing relays in accordance with the amountof varia tion in the thickness of the strip 96. These means comprise contactors 91, 98, 99, I88, I8I and I82, and resistances I83, I84, I and I85 controlled thereby. The resistance I83 is divided into three sections 038,. I83b and N3; of progressively increasing ohmic values. Similarly, the resistances I84, I85 and I85 are divided into correspondingly numbered sections of decreasing ohmic value.

Resistances I83, I84, I85 and I89 are conprogressively nected in the circuits of bucking coils 90a, 94a, 95a and 9 I a respectively.

When the variation in the thickness of the strip from the desired. thickness is sufficient merely to cause the movable contact member 86a of the contact making microammeter to move into engagement with stationary contact 86c, an energizing circuit is established for the operating coil of contactor 91, and this contactor responds to close its upper main contacts and to open its intermediate and lower contacts. The upper contacts in closing complete an energizing circuit for the operating coil oi contactor 88 and as a result of this energization, contactor 88 and its timing relay 90 function to energize the rheostat motor I01 and thereby to change the tension setting of the tension regulator I08 and to effect an increment adjustment in the tension of the strip 96. Simultaneously, the upper contacts of contactor 91 complete an energizing circuit for the operating coil of contactor 92 and as a result of its energization, this contactor and its cooperating timing relay 94 function through contactor I09 to energize the screw-down motor III! for rotation in a direction to lower the top roll 81.

Intermediate and lower contacts of contactor 91 in opening insert resistance section I03a in the bucking coil 90a of timing relay 90 and lower contact in opening inserts resistance section Na in the bucking coil 94a of timing relay 94. The result is that the time constants of timing relays 90 and 94 are varied to correspond with the amount of variation of the strip thickness from the desired gauge, thereby to produce increment adjustments in the strip tension and in the position of the top roll 8'! dependent upon the variaticn.

If the variations of the strip thickness from the desired gauge are sufficiently large to cause the movable contact member 863 of the contact making microammeter to rotate into engagement with one of the stationary contacts 08: or 86s, the contactor 98 or 99, as the case may be,

.will operate to insert resistance sections M31 or I030 in the circuit of bucking coil 90a, and resistance section I041; or I04c in the circuit of bucking coil 94a, thereby to vary the time constants of these relays in accordance with the amount of the variation of the strip thickness from the desired gauge.

If the strip thickness runs less than the desired gauge, the movable contact member 86a rotates in the opposite direction to engage the stationary contact members 86, 86: and 8B; and thereby to energize one or the other of contactors I00, IOI, or I02. These contactors in turn function in a manner similar to that already described for contactors 91, 98 and 09, to insert varying amounts of resistance in the bucking coils 95s and 9's oftiming relays 95 and 9| respectively to change the time constants of these relays in accordance with the variations in the thickness of the strip from the desired gauge. They also function to energize contactor 89 which in turn controls the motor I01 to rotate in the opposite direction thereby to effect a decrease in the setting of the regulator I08 and a corresponding increment adjustment in the strip tension; and these relays further function to effect energization of the contactor 92 which acts through contactor III to produce rotation of the,

screw-down motor H in such a direction as to raise the top roll 81.

Throughout the foregoing specification it is to be understood that increasing of tension in the strip and reducing the opening between the rolls have the same effect; namely, to decrease the gauge of the strip. Decreasing the tension in the strip and increasin the opening between the mill rolls has the opposite effect.

Although in accordance with the provisions of the patent statutes this invention is described as embodied in concrete form, it will be understood that the specific elements, apparatus and their arrangement and connection in the various modifications are merely illustrative and that the invention is not limited thereto, since alterations and modifications will readily suggest themselves to persons skilled in the art without departing from the true spirit of this invention or from the scope of the annexed claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a control. system for a strip rolling mill, means for applying tension to a strip of material as it passes through the mill, means responsive to the thickness of the strip for controlling the degree of tension applied to the strip, and means responsive to a predetermined degree of tension applied to the strip for controlling the spacing of the reducing rolls of the mill.

2. In a control system for a strip rolling mill, means for applying tension to a strip of material as it passes through the mill, means for varying the tension on the strip in accordance with vari-v ations of the thickness of the strip, means for varying the spacing of the reducing rolls of the mill, and means for operating said spacing varying means in accordance with predetermined variations of the thickness of the strip.

3. In combination, an element for operating on a length of moving material, means for tensioning said material and means responsive to variations in the gauge of said material for controlling said tensioning means to vary the tension in said material thereby to control the gaugeof said material.

4. A control system for rolling mills and the like having a pair of rolls for reducing the gauge of a strip of material and an element for tensioning the material comprising a dynamo-electric machine mechanically connected to said element, and means responsive to variations in the gauge of said material for controlling said dynamo-electric machine to vary the tension in said strip to maintain the gauge of said strip within predetermined limits.

5. A control system for rolling mill apparatus and the like having an element operating on a length of material comprising in-combination, a dynamo-electric machine mechanically coupled to said element, and means responsive to variations in the thickness of said material for controlling said dynamo-electric machine to vary the tension or said material to decrease the variations in thickness of said material.

6. A control system for rolling mill apparatus and the like having rolls for reducing the gauge of a length of material and tensioning device, comprising means for varying the opening between saidrolls, a dynamo-electric machine mechanically connected to said device, and means responsive to variations in the gauge of said material for controlling said opening varying means and said dynamo-electric machine to maintain the gauge of said material substantially constant between predetermined limits.

7. A control system for rolling mill apparatus and the like having reducing rolls and screw- 12. A control system for rolling mill apparatus and the like having a pair of .rolls for reducing the gauge of a length of material, an element for tensioning said material and screw-down mecha- 8. A control system for apparatus having an element for reducing the gauge of a length of material and a tensioning means, comprising in combination a dynamo-electric machine mechanically connected to said tensioning means, a regulator for said machine for maintaining the tension of said material substantially constant, and means responsive to variations in the gauge of said material for varying the setting of said regulator thereby to maintain the gauge of said material substantially constant Within predetermined limits. I

9. A control system for rolling mill apparatus and the like having a pair of gauge reducing rolls, a tensioning device and screw-down mechanism for varying the opening between said rolls comprising a dynamo-electric machine connected to said tensioning device, a motor for operating said screw-downs, a current regulator for said dynamo-electric machine to maintain the tension in said material substantially constant at a set value, and means responsive to variations in the gauge of said material for varying the setting of said regulator and for energizing said motor to actuate said screw-down mechanism thereby to maintain the gauge of said material substantially constant within predetermined limits.

10. A control system comprising in combination an element for reducing the gauge of a length of material, an element for tensioning said material, a motor for driving said element,

a current input regulator for said motor for maintaining the tension of said material substantially constant at a set value, means responsive to variations in the gauge of said material for varying the setting of said regulator thereby to vary the tension and to maintain the gauge of said material substantially constant,

time element means for deenergizing said regulator setting varying means after a predetermined interval of time, and means for preventing the reenergization of said regulator setting varying means until the effect of the variation of said setting has been measured by said gauge responsive means.'

11. A control system for rolling mill apparatus and the like having a pair of rolls for reducing the gauge of a length, of material, an element for tensioning said material and screw-down mechanism for varying the opening between said rolls, comprising in combination, a motor for driving said tensioning element, a current regulator for said motor for maintaining the tension of said material substantially constant at a set value, a second motor for operating said screw-down mechanism to control the gauge of said material, means for maintaining the gauge of said material substantially. constant comprising means responsive to variations in the gauge for varying the setting of said regulator and means responsive to a predetermined amount of variation of said setting for energizing said second motor tb actuate said screw-down mechanism.

nism for controlling the opening between said rolls, comprising in combination, an electric motor for driving said tensioningeiement, a current input regulator for said motor, a second motor for actuatingsaid screw-down mechanism, means for maintaining the gauge of said material substantially constant comprising means responsive to variations in the gauge of said material for varying the setting of said regulator and limit switch mechanism actuated by said setting varying means for energizing said screwdown motor, and a switching device connected to said rolls for'preventing reactuation of said regulator setting varying means for a predeterminedinterval of operation after-the preceding actuation thereof.

13. A control system for apparatus having an element for reducing the gauge of a length oi material and an element for tensioning said ma terial, comprising in combination an electric motor for driving said tensioning element, a'current regulator for maintaining the input to said motor substantially constant, a rheostat for varying the setting of said regulator, a motor for operating said rheostat, means responsive to variations in the gauge of said material for energizing said rheostat motor, time element means for deenergizing said rheostat motor a predetermined interval of time after energization, and switching means for energizing said rheostat motor to restore said rheostat to its neutral setting upon deenergization of said reel motor.

,, 14. A control system for rolling mill apparatus and the like having a pair of rolls for reducing the gauge of a length of material, an element for tensioning said material and screw-down mechanism for varying the opening between said rolls comprising a motor for driving said tensioning element, a. regulator for maintaining the current input to said motor substantially constant, a second motor for operating said screwdown mechanism, a device responsive to relatively small variations in the gauge of said material for varying the setting of saidregulator, and a second device responsive to relatively large variations in the gauge of the material for actuating said second motor to operate said screwing said tensioning element, a regulator for maintaining the current input to said motor substantially constant at a set value, a motor for operating said screw-down mechanism, a device responsive to relatively small variations in the gauge of said material for varying the setting of said regulator, a second device responsive to relatively large variations in the gauge of said material for energizing said screw-down motor, time element means for deenergizing said setting varying means and screw-down motor after a predetermined interval of time, and switching means for preventing the reenergization of said setting varying means and screw-down motor until a. predetermined length of material has passed through said rolls.

16. A control system for apparatus having an element for reducing the gauge of a length of material and an element for tensioning said material comprising in combination a motor for driving said tensioning element, a regulator for maintaining the current input to said motor substantially constant at a set value, means responsive to a variation in the gauge of said material for varying the setting of said regulator an amount dependent upon the amount of said variation. V

1'7. A control system for rolling mill apparatus and the like having a pair of rolls for reducing the gauge of a length of material, and an element for tensioning said material comprising a motor for driving said tensioning element, a regulator for maintaining the: current input to said motor substantially constant, means for maintaining the gauge of said material substantially constant comprising means responsive to variations in the gauge of said material for varying the setting of said regulator, time element means for terminating the action of said setting varying means, and means actuated by said gauge responsive means for varying the time setting of said time element means in accordance with the amount of variation in gauge.

18. A control 'system for rolling mill apparatus and the like having a pair of rolls for reducing the gauge of a length of material, screw-down mechanism for varying the opening between said rolls and an element for tensioning said material comprising a motor for driving said tensioning element, a regulator for maintaining the current input to said motor substantially constant at a set value, means for varying the setting of said regulator and means responsive to variations in the gauge of said material for controlling said screw-down motor and said setting varying means to vary the opening between said rolls and vary the setting of said regulator an amount dependent upon the variation in gauge.

19. A control system for rolling mill apparatus and the like having a pair of rolls for reducing the gauge of a length of material, screw-down mechanism for varying the opening between said rolls and an element for tensioning said material comprising in combination a motor for driving said tensioning element, a current regulator for maintaining the current input to said motor substantially constant at a set value thereby to maintain the tension in the material substantially constant, a second motor for operating said screw-down mechanism, means responsive to variations in the gauge of said material for energizing said screw-down motor and for progressively varying the setting of said regulator, time element for deenergizing said screw-down motor and said setting varying means after a time interval, and means controlled by said gauge responsive means for varying the time setting of said time element means in accordance with the amount of variation in gauge.

'20. A control system for rolling mill apparatus and the like having a pair of rolls for reducing the gauge of a length of material and a take-up reel for said material comprising in combination a motor for driving said reel, a regulator for maintaining the current input to said motor substantially constant at a set value, means responsive to variations in the gauge of said 'material forvarying the setting of said regulator to maintain the gauge of said material within predetermined limits, an electromagnetic time element device for terminating the action of said setting varying means after a predetermined interval of time, a coil on said device for controlling the time constant thereof, and means actuated by said gauge responsive means for varying the resistance in the circuit of said coil in accordance with the varations in the gauge of said material.

21. A control system for apparatus having an element for operating on a length of material and an element for tensioning the material comprising in combination a dynamo-electric machine for driving said element, means for maintaining the tension of said material substantially constant comprising a regulator for 'maintaining current of said machine substantially con-- stant at a set value, means for adjusting the tension setting of said regulator, means responsive to variations in the gauge of said material for varying the setting of said regulator, and means for limiting the operation of said setting varying means to a preselected percentage of the adjustment setting of said regulator.

22. A control system for apparatus having an element for reducing the gauge of a length of material and an element for tensioning said material comprising in combination an electric motor for driving said tensioning element, means for maintaining the tension of said material substantially constant comprising a regulator for maintaining the current of said motor substantially constant, said regulator having an operating winding connected to be responsive to the motor current and a separately excited bias winding, and means foryarying the setting of said regulator to maintain the gauge of said material substantially constant comprising a device responsive to variations in the gauge of said material and a variable resistance controlled by said device included in the current of said bias winding whereby the variation of regulator setting in response to gauge variations is limited to a predetermined percentage of said regulator setting.

FRANCIS MOHLER. 

